1. FIELD OF THE INVENTION
The present invention relates generally to a tilt-rotor aircraft, and more specifically to a means for folding the wing of a tilt-rotor aircraft for storage.
2. PRIOR ART
Many aircraft are designed with wing folding mechanisms for storage. Aircraft are often subject to limited storage areas, such as on an aircraft carrier, and require a folding wing design for efficient storage. These folding wing mechanisms must be compact, sturdy, and lightweight, so as not to hinder the flight characteristics of the aircraft. It is also desirable that the mechanism be of simple design, easy to operate, and easy to maintain.
Known methods for folding wings generally comprise splitting the wing into three segments. A central segment is affixed to the aircraft fuselage and two outer segments are hinged to the central segment. During flight operations the outer wing segments lock in a normal flight configuration. Upon landing, the outer wing segments are folded in some manner from the normal flight configuration to a storage configuration. The outer wing segments may be folded about the central wing segment and/or the fuselage.
For most typical aircraft, the folding mechanisms of the prior art are satisfactory. In one application, the outer wing segments are hinged outboard of the propulsion systems, and are folded rearward parallel to the fuselage. Each hinge point therefore only supports the weight of the outer wing segment. The aircraft remains stable in a stored configuration as the shift in the aircraft center of gravity is substantial only if the weight of the outer wing segment is a significant fraction of the total vehicle weight. In a second application, the outer wing segments are again hinged outboard of the propulsion systems and are folded over, and generally parallel to, the central wing segment. The segments may either lay flat and substantially overlap, or may be upright, in a triangular configuration. As with the first application, each hinge point supports only the weight of the outer wing segment. The aircraft remains stable in a stored configuration as the shift in the aircraft's center of gravity is usually not substantial.
The known wing folding mechanisms create substantial design penalties for a tilt-rotor aircraft. Firstly, a tilting rotor-prop assembly is mounted on each wing tip. The hinge point of a prior art design would therefore have to withstand the substantial bending moment produced by a wing tip mounted tilt rotor-prop assembly (including the rotors, the engine, and the transmission). Secondly, the hinge must accommodate the tilt-rotor wing cross-shafting, fuel system, and control systems. Thirdly, the folding of the massive tilt-rotor wing segment causes a large shift in the center of gravity of the aircraft. Folding the outer wing segments backward parallel to the fuselage results in a substantial rearward shift in the center of gravity. This shift must be accommodated by the structure and location of the landing gear. Folding the outer wing segments directly over the center wing segment raises the center of gravity, making the stored aircraft less stable. Fourthly, a large force is required to lift the tilt-rotor-prop assembly above and about the hinge point. These structural and weight demands on the hinge point make the traditional wing segment folding mechanisms impractical for a tilt-rotor wing aircraft.
For these and other reasons, the presently known wing folding mechanisms are unsatisfactory for use on a tilt-rotor aircraft. A need exists for a simple, compact, lightweight wing fold mechanism for a tilt-rotor aircraft.